The invention relates to hydrocarbon processing. In one aspect, the invention relates to a process for converting mercaptans found in hydrocarbon streams into disulfides.
Mercaptans are undesirable in hydrocarbon products because of odor and discoloration. The effects of these compounds can be eliminated by reacting two mercaptans to form one disulfide compound, or in effect, connecting the two terminal end sulfur atoms. The reaction is usually the final stage in gasoline refining. Industly follows many methods for this process, usually involving several steps and vessels. Due to the low cost of operation, caustic treating is the preferred process.
During caustic treating, gasoline is injected with air and allowed to come into contact with a caustic solution. The caustic can contain a catalyst which promotes the chemical reaction. The reaction is based on the principles of mass diffusion, or the movement of molecules from one substance into another. The molecules of oxygen, caustic, and mercaptans must all come into contact with each other to react. The mercaptan molecules are dispersed throughout the gasoline, and thus, must travel through the gasoline until it reaches contact with the caustic and oxygen.
As the reaction takes place, oxygen is consumed. The amount of required oxygen greatly increases as the concentration of mercaptan in the gasoline increases. At a given temperature and pressure, air has a constant solubility in gasoline, therefore, regardless of the concentration of mercaptans, the concentration of oxygen is constant. When the soluble oxygen has been consumed, the reaction stops short of treating all the mercaptans. In the prior art, the problem of limited oxygen solubility was partially compensated for by increasing system pressure.
A process for treating hydrocarbon liquids which contain high concentrations of mercaptans would be desirable. A process for treating hydrocarbon liquids which contain high concentrations of mercaptans in existing low pressure equipment would be even more desirable.